Receiver for short waves



y 6, 1952 A. VAN WEEL 2,595,997

RECEIVER FOR SHORT WAVES Filed July 12, 1946 4 INVENTOR.

ADFLBERT K4N WEEL BY 5 e v ATTORNEY I Patented May 6, 1952 RECEIVER FOR SHORT WAVES Adelbcrt van Weel, Eindhoven, Netherlands, as-

signor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application July 12, 1946, Serial No. 683,001 In the Netherlands October 27, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires October 27, 1963 1 Claim. 1

This invention relates to a circuit arrangement for mixing ultra-high frequency oscillations, which circuit is tunable over a large range of frequencies and in which one of the oscillations to be mixed is fed in the same phase and the other frequency through a Lecher system in push-pull connection to the input electrodes of two discharge systems. This mixing method yields great advantages more particularly in transmitting ultra-high frequencies, since it permits the obtainment of a lower input damping and a better signal-to-noise ratio.

As a rule, however, such circuits are suffering from the drawback that the input impedances of the discharge systems, more particularly in the transmission of ultra-short waves, have only a small value, due to which the voltage having the freqeuncy of the oscillations supplied in the same phase, which appears between the input electrodes of each tube, often becomes too low. In the circuit to which the invention relates, in order to feed as high as possible a voltage having this frequency to the input electrodes, the single phase circuit constituted by,

the pairwise parallel connected impedances of the two halves of the push-pull circuit and the parallel connected input impedances of the two discharge systems, jointly with the impedances common to the input circuit of the two systems,

is tuned to the frequency of the oscillations supplied in the same phase.

In tuning the circuit over a large range of frequencies it is generally necessary to adjust two resonant circuits viz. the push-pull circuit to the frequency of the oscillations supplied in push-pull and the single phase circuit to the frequency of the oscillations supplied in the same phase. The invention provides an expedient for combining these two tunings.

According to the invention the aforesaid Lecher system is designed in such manner that by controlling this system the push-pull circuit is tuned to the frequency of the oscillations supplied in push-pull and the said (single phase) circuit is tuned at the same time to the frequency of the oscillations supplied in the same phase.

If the intermediate frequency used in the mixing circuit is not very high, so that the fre quencies of the oscillations to be mixed are slightly different from each other, this simultaneous tuning can be ensured by giving the Lecher system such proportions that the product of the surge resistance and the terminal capacity of the two Lecher lines with respect to one another is equal or substantially equal to the product of the surge resistance and the terminal capacity of the two Lecher lines jointly with re spect to earth.

If the said terminal capacities consist exclusively or almost exclusively of the input impedances of the discharge systems the Lecher system is preferably designed in such a manner that the surge resistance of the two Lecher lines with respect to one another is about four times as high as the surge resistance of the two Lecher lines jointly with respect to earth.

The invention will be more fully explained by reference to the accompanying drawing in which one embodiment thereof is represented by way of example.

The sole figure represents a mixing circuit arrangement embodying the invention and forming part of a superheterodyne receiver for short waves. The incoming oscillations are supplied in push-pull and the local oscillations in the same phase to the control grids of two discharge systems T and T. The oscillations picked up by a dipole antenna D, D" are fed to "two conductors L1 and L1 forming part of a Lecher system which is tunable to the frequency of the incoming oscillations by means of a short circuit bridge K. The short-circuit bridge K and the junction of the cathodes of the two discharge systems are connected to earth. The end 01' the Lecher system, which is located on the side of the short-circuit bridge K remote from the discharge systems, is made inoperative by termination with a resistance R2 whose value corresponds to the surge resistance of the Lecher lines L1, L1 with respect to one another. Similarly the end of the Lecher system, constituted by the two Lecher lines in parallel-connection with respect to earth is terminated by the surge resistance in question. To this end the middle of the resistance R2 is connected to earth through the intermediary of a resistance R3. In this case it may occur that the middle of the resist ance R2 should be directly connected to earth. In the drawing the input impedances of the two discharge systems are represented by the capacities C1, C1. The two triodes T, 'I may advantageously constitute a single tube and may have a common cathode, if desired.

A resonant circuit tuned to the intermediate frequency and consisting of two coils La, La" and two condensers C2, C2" is connected in push-pull arrangement to the anodes of the two triodes. In series with coils L3, L3" are provided high-frequency chokes L2, L2 which serve to prevent a transmission of the incoming high-frequency oscillations to the receiver parts next to the mixing circuit arrangement. The junction of coils L3, L3 is connected to earth through a condenser C3, which practically constitutes a short-circuit in regard to the intermediate frequency oscillations, and through a resistance R1 to the positive terminal of a source of anode potential (not represented). Furthermore the coils L3, L3 are inductively coupled with another intermediate frequency circuit L4, C4, from which is taken the output voltage of the circuit. The junction of condensers C2, C2" is connected through an inductance L2 to the cathodes of the two triodes.

Owing to the presence of coil L2, which is exclusively traversed by a current having the frequency of the local oscillations, a positive backcoupling is obtained in regard to the local oscillations. In fact, due to the voltage loss across this coil an alternating anode voltage having the frequency of the local oscillations and lagging by 90 with respect to the alternating controlgrid voltage appears between anode and cathode of each triode T, T. As a result thereof, currents having this frequency, which are in phase with the alternating control-grid voltages and consequently bring about negative damping of the single-phase circuit, are passing over the anode control-grid capacities designated C5, C5 in the drawing. In the present case this negative damping is sufficient to render the circuit self-oscillatory, so that a separate local oscillator can be dispensed with.

To supply as high as possible a voltage having the frequency of the local oscillations to the input electrodes the single-phase circuit constituted by the parallel-connected impedances of the lines L1 and L1 with respect to earth and the parallel-connected input impedances C1 and C1" of the two triodes, is tuned to this frequency. As a rule this tuning can be ensured only by interposing a variable impedance, for instance between the junction of the cathodes and earth.

However, such a circuit exhibits the drawback that the tuning of the receiver requires the control of two variable impedances viz. the tuning of the push-pull circuit by means of the short-circuit bridge K and the tuning of the single-phase circuit by means of the said impedance (not represented), between the junction of the oathodes and earth.

According to the invention this complication can be avoided by designing the Lecher system L1, L1 in such manner that the adjustment of this system involves the simultaneous tuning of the push-pull circuit to the frequency of the incoming oscillations and of the single phase circuit to the frequency of the local oscillations. In effect, the two Lecher lines L1, L1" not only constitute a Lecher system with respect to one another, but the two lines in parallel connection likewise constitute a Lecher-system with respect to earth. By shifting th short-circuit bridge K, which is connected to earth, the two systems can be tuned simultaneously, provided the proportions of the Lecher lines with respect to one another and of the Lecher lines with respect to earth satisfy a definite condition. In fact, the tuning of a short-circuited Lecher system depends on the product of its surge resistance and the impedance provided over the not short-circuited end, which impedance is usually a capacity (terminal capacity). In the case under view, as far as the push-pull circuit is concerned, this terminal capacity is constituted by the series-connection of the two input capacities of the discharge systems C1 and C1" as far as the singlephase circuit is concerned it is constituted, in contradistinction thereto, by the parallel connection of the capacities C1 and C1". Consequently, for a simultaneous tuning of the pushpull circuit to the incoming oscillations and of the single-phase circuit to the frequency of the local oscillations it is necessary that the product of the surge resistance of the two Lecher lines L1, L1 with respect to each other and the capacity of thesaid series-connection should be matched- -to the frequency of the incoming oscillations and that the product of the surge resistance of the two Lecher lines L1, L1" in parallel connection with respect to earth and the capacity of the said parallel connection should be matched to the frequency of the local oscillations.

If the intermediate frequency of the receiver is not very high and consequently, the frequency of the local oscillations substantially corresponds to the frequency of the incoming oscillations, these two products should be about equal.

Furthermore, if the two terminal capacities consist exclusively or almost exclusively of the input impedances of the two discharge systems, such as is indeed the 'case in the represented circuit, the surge resistance of the two Lecher lines should be four times as high as the surge resistance of the two Lecher lines jointly with respect to earth, since in this case the terminal capacity constituted by the series connection is four times as small as the terminal capacity constituted by the parallel-connection of the input capacities C1, C1.

In a practical embodiment of the present invention one may proceed in such manner that the Lecher system L1, L1" is located opposite an earthed metal plate, and the distance between the Lecher system and the said plate being variable. By adjustment of this distance the surge resistance of the Lecher system, which is constituted by the parallel connected Lecher lines L1, L1" and the metal plate, may be adjusted to the desired value.

As analternative the terminal capacities may be variable so as to achieve the desired value of the product of surge resistance and terminal capacity. Thus, for instance, the input capacity of the push-pull circuit may be increased by providing a condenser between the two control grids, or the input capacity of the single-phase circuit may be decreased by interposing a condenser between the junction of the cathodes and earth. However, these expedients are less advisable than the aforesaid adjustment of the ratio of the surge resistances, since the input impedance of the circuit falls off due to the increase in input capacity of the push-pull circuit, and the cathodes are no longer earthed due to the insertion of a condenser between the cathodes of the discharge systems d earth.

The connection of the short-circuit bridge K to the metal plate must be designed. in such a manner that this connection acts, in effect, as a short-circuit bridge in regard to the Lecher system constituted by the parallel connection of the line L1, L1 with respect to earth.

The embodiment shown in the figure indicates the use of two triodes, but the invention is not so limited. Any discharge system could be used which provides similar characteristics. tetrodes, pentodes, etc, could be used or a duo Diodes,

type of tube such as a duotriode would operate equally as well.

If desired, the junctions between the dipole antenna and the Lecher system L1, L1" may be variable to permit optimum matching of the antenna to the discharge systems for every frequency to which the receiver is tuned.

Sometimes it is advisable to undamp the pushpull circuit, which may be effected by inserting an inductance in each anode circuit between the anode and the junction of coil L2 and the con denser C2 and coil L2" and the condenser C2 respectively.

In the drawin the push-pull circuit is provided between the two control grids of the triodes T and T", the cathodes being interconnected. As an alternative, however, the push-pull circuit may be provided between the cathodes and the control grids may be interconnected.

In the embodiment shown in the figure, the incoming oscillations are supplied in push-pull connection and the local oscillations in the same phase to the input electrodes of the discharge systems, but it is also possible to feed the local oscillations in push-pull and the incoming oscillations in the same phase to the input electrodes.

What I claim is:

A high frequency mixing circuit arrangement tunable over a wide frequency band, comprising first and second electron discharge mixer elements each comprising a cathode, a control grid and an anode, a first Lecher system comprising two Lecher lines each connected to the control grid of one of said mixing elements, said Lecher system having a given surge impedance and having a given terminal capacity consisting essentially of the input capacitance of said mixer elements connected in series, means coupled to said Lecher lines to apply a signal wave to said Lecher lines in push-pull relationship, a second Lecher system comprising said two Lecher lines and a conductor in spaced relationship to said Lecher lines, said conductor being coupled to the cathode of said mixing elements in the same phase relationship, means to apply an oscillator wave to said two Lecher lines in the same phase relationship, said latter means comprising an inductive reactance having one end thereof coupled to said cathodes and having the other end thereof coupled to said anodes, said second Lecher system having a terminal capacity consisting essentially of the input capacity of said mixer elements connected in parallel and having a surge impedance substantially equal to one-fourth of the surge impedance of said first Lecher system, a short circuit bridging member interconnecting said Lecher lines and said plate member, said bridging member being movable along the length of said Lecher lines to vary the efiective length of said Lecher lines to thereby simultaneously vary the resonant frequencies of said first and said second Lecher systems through a given frequency range while maintaining a substantially fixed frequency difference between said resonant frequencies, and means coupled to said anodes in push-pull relationship to derive therefrom an intermediate freuency wave having a frequency substantially equal to said fixed frequency diiierence.

ADELBERT VAN WEEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,011,943 Lindenblad Aug. 20, 1935 2,211,003 Conklin Aug. 13, 1940 2,260,844 Thomas Oct. 28, 1941 2,307,074 Pray Jan. 5, 1943 2,382,693 Dallenbach Aug. 14, 1945 2,427,241 Hofweegen Sept. 9, 1947 2,479,537 Fyler Aug. 16, 1949 

